SAN FRANCISCO—Around here, the first reaction is to duck. And then to glance around, to see if the earth is shaking, if there are cracks in the cement walls and deep craters opening up in the ground.

Around here, more than anything folks know not to panic. So when Candlestick Park slipped into complete darkness at 5:19 p.m. PT Monday—inspiring scary flashbacks to the deadly Earthquake of ’89 that struck the Bay Area just as a World Series game was about to begin—tens of thousands of football fans who had barely settled into their seats did something quite extraordinary.

They gasped as one, and then they waited. Calmly. Patiently. Was the dark drama part of a pregame show? Players from both the San Francisco 49ers and the Pittsburgh Steelers were still in their pitch-black locker rooms. Cheerleaders stood on the field, motionless shadows, while the scoreboards flashed nonsensical images.

Soon word spread that a transformer near the stadium in South San Francisco had blown out and city officials were working to repair it. For about 15 minutes, darkness ruled, fans stayed cool and everyone seemed to give silent thanks that the unthinkable hadn’t happened. Eventually emergency generators clicked on to illuminate the field with temporary lightning, and the party atmosphere that had been at a low roar before the blackout struck clicked into full rage.

On the eve of making his “Monday Night Football” debut as 49ers coach, Jim Harbaugh had said: "It's one of the NFL's biggest stages, brightest lights. Football players in general, going back to high school, like playing under the lights. It's a thrill."

And so it was. The number of Steelers fans at the 'Stick was something to behold. Several thousand were here decked out in their black-and-gold wardrobe, waving Terrible Towels. They had come to witness the clash of two playoff-bound teams, with much at stake. The 10-3 49ers looked to secure a crucial bye for the wild-card round and maintain their status as the No. 2 seed for the NFC playoffs. The 10-3 Steelers, with a wounded Ben Roethlisberger due to start, hoped to refine their bid for a fourth Super Bowl appearance in seven seasons.

One of the oldest stadiums still standing in North America, the 'Stick is a creaking wind tunnel with loads of charm. On Oct. 17, 1989, just as the San Francisco Giants and the Oakland A's were stretching and taking batting practice here before Game 3 of the World Series, a major quake caused by a slip in the San Andreas Fault struck at 5:04 p.m.

Viewers around the world heard Tim McCarver’s distracted narration of taped highlights, followed by Al Michaels saying, “I'll tell you what—we're having an earth—.” Then the feed from Candlestick Park was lost. Sixty-three people were killed throughout Northern California, thousands were injured and an estimated 20,000 left homeless.

“That’s the first thing I thought of,” said a man who gave his name as Sam Smith, as he stood with his 10-year-old son in an uncovered portion of the 'Stick Monday night, waiting for the lights to be fixed. “If you’re from the Bay Area, you know what to do in the event of an earthquake. I’m just incredibly thankful we’re not having one."